The present invention relates to a metallized polyester film capacitor. More particularly, it relates to a metallized polyester film capacitor with excellent moist heat resistance.
Polyester films such as polyethylene terephthalate films have been popularly used as base film of capacitors because they have excellent mechanical, thermal and electrical properties.
However, with development of various electronic machines in recent years, further improvement of properties of polyester films has been demanded. One of the required properties is long-term stability of moist heat resistance. A metallized polyester film is disadvantageous in stability of adhesion of the base film to deposited metal, especially in an environment of high temperature and high humidity. When the capacitor is exposed to a high temperature and a high humidity, moisture penetrates at the interface between the base film and the deposited metal, so that capacitance of the capacitor lowers with passage of time. Thus, improvement of moist heat resistance of capacitors has been demanded for long-term durability of the capacitor.
Japanese Patent Application Laid-Open (KOKAI) No. 4-245414 (1992) discloses a metallized polyester film capacitor using a polyester film having a polyester polyurethane coating layer, which is described as having excellent moist heat resistance.
However, even if the resin composition disclosed in the above Japanese KOKAI is used to the capacitor, satisfactory capacitor performance thereof can not be retained for a long term under a hot and humid environment.
Recent development of various electronic machines is remarkable and the capacitor are increasingly used under severer environments, so that the request for long-term stability of moist heat resistance, is further increasing.
As a result of studies by the present inventors, it has been found that by using as a base film, a polyester film having a coating layer composed of a polycarbonate polyurethane, the obtained capacitor comprising a metallized polyester film shows excellent moist heat resistance for a long term. The present invention has been attained on the basis of this finding.